http://pastebin.com/idHvkgUi

Thanks for reporting this on such short notice! It could've really turned into a horrible mess.

did this get a stealth update?

Pretty much. Did a re-release on 1.8.9-1.9.0.

rereleases without version changes are hell on pack devs, and screwup auto updaters such as those used by ATL, FYI.

If the stealth update is released 5 hours after the original one (which at the time has received 20 downloads), there should be next to no impact. Besides, I hardly do stealth updates, only when the new version breaks at startup (and was released less than 8 hours ago).
I also make a note that there was an issue causing there to be a re-release (which I unfortunately didn't spread too much this time).

my auto updater, through ATL, tracks by version number.

It DLs automatically when there's an update, and that file is what gets referenced by a pack who uses their auto update feature. Meaning as far as they can tell they have the most up to date version, because, you know, that's what version numbers mean.

In the event of a stealth update, while no one knows you needed to fix anything, no one knows anything they see breaking is fixed. Then they think your mod is buggy, and not how cool it is. Making mistakes and fixing them, makes you look more reliable / less wrong in the long run.